A cluster in salience space
The phrase “a cluster in thingspace” implies that, even as concepts are fuzzy bundles of extensions rather than clearly boundaried intensions, they are organized and grouped together by virtue of some “real,” formal, objective similarity. This is misleading.
Rather, members of most conceptual sets are grouped together because they are similar or patterned in ways which are perceptually and pragmatically salient to human beings in a specific culture of distinction and practice.